The present invention relates to an electrical conductor and to a method of fabricating such a conductor.
The structure, and the method of fabrication, of flexible multi-filament electrical conductors has not changed substantially in over 50 years. The individual filaments have been of circular cross section and have been manufactured in a time-consuming, energy- and capital-intensive manner. As is well known to those skilled in the art, an array of mineral processing and pyrometallurgical steps and procedures has been employed to yield copper in the form of "wire bar," which is of relatively hefty cross section. A further array of mechanical steps is then required to reduce the wire bar to the individual fine filaments that are desired. Typically, these mechanical steps include a multiplicity of drawing steps through a large series of dies of progressively smaller size. The drawing steps may be, if required, interspersed with one or more annealing steps. As is also well known to those skilled in the art, as the desired filament diameter is reduced, the capital expenses per pound of material processed required to achieve these mechanical steps increases rapidly.
Furthermore, once the desired circular cross sectional filaments have been obtained, the twisting together of such filaments results in an electrical conductor in which the void content accounts for approximately 25% to 30% of the cross sectional area. This, of course, results in a relatively large diameter stranded wire for a given current carrying capacity, a feature which increases insulation expenses and renders the conductor bulky and difficult to utilize in various electrical systems.
A relatively recently proposed modification of the final steps of manufacturing conventional stranded wire is disclosed in U.S. Pat. No. 3,786,623. There, a circular cross section wire is produced in a conventional manner having a diameter in the range of 1.5 mm to 15 mm. This relatively large wire is flattened to a strip or band which then passes through a shearing device to yield a number of individual strands which are then twisted together, in a conventional manner to form the final wire. This proposal, of course, does not eliminate the great majority of the pyrometallurgical and mechanical processing steps of conventional techniques and apparently has as its main alleged advantage the elimination of the large masses of the several reels supported on the twisting machine.
Canadian Pat. No. 869,065, issued Apr. 20, 1971, entitled "Method of Producing Copper Wire" teaches various techniques for producing strips of copper wire by electrodeposition in a form suitable for feeding into conventional wire drawing apparatus. Much of the teaching of the patent is directed to achieving a desirable cross sectional shape for the individual wire strands produced by the electrodeposition. One briefly mentioned technique for producing a desirable cross sectional shape is the welding, by means of pressure, of two or more of the copper strands formed through electrodeposition.
An initial step in the fabrication of stranded wire, according to the present invention, involves the electroformation of electrically conductive filaments. Electroformation of electrically conductive filaments has, of course, been known for some time, but has been employed principally in the preparation of various speciality wires and typically has been followed by drawing and/or plating steps to form circular cross section filaments usable as very fine gauge wire. An example of a system for electroformation of metallic strands can be found in Wang U.S. Pat. No. 3,929,610, issued Dec. 30, 1975, entitled "Electroformation of Metallic Strands," assigned to the Assignee of the present invention, and incorporated herein by reference.
In view of the above discussion, it is a principal object of the present invention to provide a flexible elongate electrical conductor, and a technique of manufacturing such a conductor, which is conducive to reductions in the capital and energy requirements necessary to produce such a conductor.
It is a further object to provide such a conductor, and such a method, conductive to the provision of electrical conductor having improved mechanical and/or electrical properties compared to conventionally produced conductor of equivalent current rating.